The present invention generally relates to gas turbine engine systems and, more particularly, to combustor assemblies for gas turbine engines.
Combustor assemblies are integral components of gas turbine engines. The combustor assembly may be positioned in flow communication with a compressor, a fuel injector and one or more turbines. During engine operation, pressurized air from the compressor and fuel from the fuel injector may enter the combustor. The resulting fuel/air mixture may be ignited to produce a high temperature combustion gas stream. The hot combustion gas then flows downstream to the turbines for energy extraction.
The extreme temperature environment resulting from the hot combustion gas stream limits the useful operating time and ultimately component life of the combustor and turbines. The turbine and combustor components are very sensitive to variations and extremes in temperature. Methods for mitigating the negative effects of the high temperature combustion gas have been disclosed.
A multihole patch for a combustor liner has been disclosed in U.S. Pat. Application No. 2003/0200752. In the described method, patches of dissimilar sized holes are used for cooling the liner wall. Cooling of the walls is provided by a combination of orifices behind nuggets and groups of small holes drilled at an angle in regions requiring augmented cooling. Although the described method may reduce the thermal stress to the combustor liner, a reduction in the thermal stress experienced by the downstream components is still needed. Further, a reduction in gas stream temperature variation is also needed.
Another combustor liner has been disclosed in U.S. Pat. No. 6,260,359. The described liner is provided with two rows of close-coupled dilution holes at different axial positions. The first row of holes (primary) is of uniform size and has an equiangular spacing. The second set of dilution holes is of varying size to minimize hot-streaks formed by the fuel injectors and to provide a uniform circumferential pattern factor (temperature variation). Although the described combustor liner may reduce temperature variation across the plane of the combustor outlet, the disclosed combustor is an annular combustor and does not address the need for reductions in scroll wall temperatures, as annular combustor configurations do not include scrolls.
A combustor for a turbine engine is described in U.S. Pat. No. 6,606,861. The disclosed combustor is provided with major and minor dilution jets to regulate the spatial temperature profile of the exhaust gases from the combustor. Although the disclosed combustor may reduce temperature variation, the described combustor is also an annular combustor and, therefore, does not address the need for scroll wall temperature reductions. An annular combustor or can-annular (separate cans in a common annulus) arrangement may not be suitable for some turbine engine applications.
A single can and scroll type configuration may be desirable for some applications. The single can and scroll configuration has a single fuel injector. The need for only one fuel injector may simplify engine design, maintenance, and repair, thus reducing the associated cost. The single can and scroll configuration allows for the use of a fuel injector that is larger than the fuel injectors suitable for use in annular combustors. This is advantageous in ameliorating fuel injector coking. Fuel injector coking is a function of the dimensions of the fuel injector's internal passages. Larger fuel injectors have larger internal passages and therefore are more resistant to coking. Yet another advantage of the single can and scroll configuration is that the thermal stress on downstream components is reduced due to the better pattern factor through the scroll.
Although there are several advantages of the single can and scroll arrangement, one disadvantage is that the scroll has a relatively large surface area. Depending on the engine operating cycle, the scroll may require air cooling and sufficient air may not be available to allow effusion or film cooling over such a large surface. Additionally, for some applications, the conventional dilution cooling arrays have met with limited success. Conventional dilution cooling arrays comprise equi-sized dilution orifices and may provide inadequate penetration of cooler air to the core of the hot combustion gases in some applications. Although penetration of the dilution air may be increased by increasing the combustor pressure drop, this is not a desirable option since the pressure drop represents a parasitic loss on the engine performance.
As can be seen, there is a need for improved combustor assemblies. Additionally, improved can/scroll combustors are needed wherein the scroll cooling requirements are reduced. Further, dilution cooling arrays having improved core penetration without an increase in combustor pressure drop are needed. Combustor improvements allowing for easy retrofit to existing designs also are needed. Improved combustors are needed wherein temperature variation across the combustor exit plane is reduced.